The lattice dynamics of crystalline Li 22 Pb 5 is studied by means of computer simulations. The calculated spectrum shows several bands corresponding to modes in which only the light atoms execute motions. The spectrum of acoustic modes is found to be well separated from the high-frequency bands and is in all cases confined to frequencies below 4 meV. The results are shown to provide a clue for the understanding of the origin of the strong anomalous dispersion features found in the melt by

more »

... iment ͓Phys. Rev. Lett. 80, 2141 ͑1998͔͒ and molecular dynamics simulations ͓Phys. Rev. E 58, 4568 ͑1998͔͒. ͓S1063-651X͑99͒10003-5͔ PACS number͑s͒: 62.60.ϩv, 63.50.ϩx, 62.65.ϩk PRE 59 3213 COLLECTIVE DYNAMICS ON A CRYSTAL COMPOSED . . . PRE 59 3215 COLLECTIVE DYNAMICS ON A CRYSTAL COMPOSED . . . FIG. 3. A representative sample of J l (Q,E) spectra corresponding to directions ͑a͒ ͓00͔, ͑b͒ ͓0͔, and ͑c͒ ͓͔. The corresponding momentum transfers are shown as insets. 3216 PRE 59 R. FERNÁ NDEZ-PEREA et al.